The following situation regarding the loading and unloading process prevails in connection with loading platforms:
The platform, which is pivotable around a horizontal axis at its ramp end, is moved into its highest position by appropriate spring-assisted drives. There, the extension is flipped out by means of appropriate devices and an operator moves onto the platform. Because of the additional weight, the platform is lowered onto the load bed of the vehicle to be loaded or unloaded. A hold-down mechanism is used, so that the platform always follows the vertical movements, up as well as down, of the vehicle generated by the in and out movements of the loading equipment.
Existing systems operate with a toothed rack which can be latched. Downward movement takes place without resistance. If the load bed of the vehicle is raised, a built-in spring allows the platform to be slightly raised. If the platform is raised too far, an unlatching chain undoes the latch and the toothed rack is lifted out of the lock one tooth at a time. The disadvantage of the toothed rack system lies in the loud noise generated, as well as the non-continuous and, because of the teeth, jerky movement, when the platform is lifted. The manufacture of these systems is also relatively expensive.
Such a mechanism, operating on the basis of oil and gas pressure, is known from European Patent Disclosure EP-A 0 428 805. However, this, too, is comparatively expensive to manufacture.